"He took me out of the match," Raonic said. "Not too much I could do. He just did a lot of things too good today."

The third-seeded Murray converted 4 of 12 break points and never faced one. After weathering six aces across Raonic's first three service games, Murray only allowed eight the rest of the way.

"You start to see things after a few games. He started serving a lot of big serves. I was just trying to react as quickly as possible," Murray said in an on-court interview at Arthur Ashe Stadium. "Sometimes they fly past you, sometimes you get a racket on them - and I got a racket on them."

Raonic's 14 aces were less than half as many as he accumulated in any of his first three matches this year at Flushing Meadows, when he hit 30, 30 and 29.

"I used a lot of variation tonight. Milos has a huge game, massive serve. I had to guess on some of the serves," Murray said. "I got lucky a few times."

Next for Murray is a match against No. 12 Marin Cilic. Murray leads their head-to-head series 6-1, but his only loss to Cilic came at Flushing Meadows in the fourth round in 2009.

"When I feel well," Cilic added, "I feel I can match up with anybody."

Murray probably thinks the same way, especially with the confidence boost he picked up with his gold medal last month.

He's yet to win the last match at a Grand Slam tournament, though: Murray and his coach, Ivan Lendl, are the only men to lose their first four major finals.

Murray only had played once before against Raonic, who was trying to become the first Canadian man in a major quarterfinal in the Open era, which began in 1968.

Going in, it appeared to shape up as an intriguing matchup, pitting Raonic's tough-as-can-be serve against Murray's good-as-it-gets returning skill and pinpoint passing shots.

Raonic entered the U.S. Open leading the ATP in several key serving-category percentages - service games won (93), first-serve points won (83), break points saved (75) - and second in total aces only to 6-foot-9 American John Isner, who lost in the third round in a match that ended at a tournament-record-tying 2:26 a.m. Monday.

Murray, meanwhile, tops the tour in points won returning second serves (56 percent) and is fifth in return games won (31 percent).

Giving himself a better chance at dealing with Raonic's speedy offerings, Murray stood way, way back behind the baseline while preparing to hit returns. And that worked, allowing Murray to blunt Raonic's serves that consistently arrived at more than 130 mph.

On the very first point, Murray got back a 120 mph serve and then delivered a backhand passing winner down the line, a sign of things to come.

At 4-all, Raonic gave away two points with a pair of double-faults, and Murray broke for the first time by carving a drop shot at a tough angle that the Canadian couldn't get to. Showing he can sling it, too, Murray served out the set with a 138 mph service winner.

Murray won 20 of 24 points on his serve in the first set. He capped the second with an ace that clipped a line, and ended things with a 129 service winner on match point.

"Really important to serve well, the deeper you go in the tournament," Murray said. "Conserves a lot of energy."

Fish missed about two months this season because of an accelerated heartbeat and had a medical procedure in May. His agent, John Tobias, said "we are not 100 percent sure what the issue is and if it is related to his previous issues."

"I was reluctant to do so, but am following medical advisement," Fish said about his withdrawal in a statement. "I had a good summer and look forward to resuming my tournament schedule in the fall."

The 30-year-old American's third-round match against Gilles Simon went five sets, lasting more than 3 hours and ending after 1 a.m. Sunday. Afterward, the 23rd-seeded Fish did not appear at a news conference. Tournament officials said he was getting treatment, but didn't give specifics.

"I am really sorry for Mardy. I just want to wish him a speedy recovery," Federer said in a statement. "We all want to see him back on tour soon."